What is the best way to get circular/linear signals?

[nycrich]

I have a DMX741U lnb on my 6 ft dish. It receives C and Ku. To get circular signals on NSS7/NSS806 I need to put in the dielectric plate. This causes major signal degradation on linear sats. I would like to get an lnb that can receive both linear/circular signals the same time without significant signal loss on C/Ku. I understand that Ku is all linear. I am hoping to use this on my Viewsat 9000HD, and AZBOX that is arriving soon.
I know there are feedhorns like the Chaparral Corotor Plus that allows simultaneous reception of linear/circular signals on C and Ku. For those of you using this is there any signal loss trying to get reception of circular and linear the same time. Do you need to use a dielectric plate also?? Which is the best way to get linear/circular reception with an lnb? I have a Gbox that could control the skew/motor.

 

[Mr Tony]

I'm going to move this to the C-Band area...maybe some of our experts can help with that question.

 

[Anole]

I have a DMX741U lnb on my 6 ft dish. ...
To get circular signals on NSS7/NSS806 I need to put in the dielectric plate.
This causes major signal degradation on linear sats. ...

I know there are feedhorns like the Chaparral Corotor Plus that allows simultaneous reception of linear/circular signals on C and Ku. ...
Which is the best way to get linear/circular reception with an lnb?

Someone has talked about this before, and I was hoping they'd chime in with an answer.
I tried to search for an appropriate thread, but didn't find the info.
What I did find was this thread by Pendragon, where he mounted two feedhorns, one for circular and one for linear, to get good reception.

I have a Gbox that could control the skew/motor.

The Gbox just controls the motor to move the dish across the sky.
Sadoun was going to work on a box that did both, but the economy being what it is, that project is on hold.

If you need to control a skew motor on the feedhorn, consider a Pansat 3500 or 2700 (?) DVB receiver, or ...

There was an article by Equant some time back where he controled the skew motor with his own microcontroller.
But, it's not directly applicable to your needs: Polarotor Servo Controller Design

...or... an Analog receiver... or...

edit:

The corotor II plus wideband is c/ku linear and c-band circular.

...taken from this discussion.

BUT, the Chaparral web site says it uses a dielectric plate, so I'm lost!

 

[pendragon]

If you want a single feed to do both linear and circular for C-band without venturing out to your dish, you're pretty much stuck with the wideband Corotor II+. It has a dielectric plate that has to be aligned exactly vertical or horizontal to be able to get all four polarizations. If the rotor probe is vertical or horizontal, you get the linear polarizations. If it is 45 degrees plus or minus, you get the circular polarizations. Obviously you need a receiver or a custom skew controller to mange these four positions. I've never tried a WB Corotor II+, but in private and public communications with others that have the equipment and expertise to know, this feed has some losses and you will not get the same CNRs as with high quality orthomode feeds.

The dielectric insert you have is of course the second option, which requires manual configuration to switch between linear and circular polarization. As you have found, this causes losses, probably fairly similar to the WB Corotor II+. It's the same basic concept.

If cost is no object, then my recommendation is to follow the link to my siamese feed thread that Anole provided. By offsetting dedicated linear and circular feeds the way I did, there are very tiny offset losses and each feed can do what it does best. I combined the best orthomode feeds I could find for each, and the performance is very impressive. The ADL circular ortho is a wonderful feed and I tend to believe their claims that the quarter wave plate has lower losses than a dielectric insert based on some measurements I've done. But it costs around $500. You could slap two of the types of feed you already have, one with the dielectric insert and the other without, but I can't say how much you will lose on the circular side.

 

[Anole]

... the wideband Corotor II+.
It has a dielectric plate that has to be aligned exactly vertical or horizontal to be able to get all four polarizations.
If the rotor probe is vertical or horizontal, you get the linear polarizations.
If it is 45 degrees plus or minus, you get the circular polarizations.

Oh, thanks! Now I get it. -
What a major pain in the . . .

Obviously you need a receiver or a custom skew controller to mange these four positions.

Well, with some clever modifications, the servo controller Equant designed, could do the job.
With one switch input, it could move between linear and circular, changing H/V or R/L by detecting the voltage.
(but , that's a product that exists only in our minds, and will never see the light of day )

I've never tried a WB Corotor II+, but in private and public communications with others that have the equipment and expertise to know, this feed has some losses and you will not get the same CNRs as with high quality orthomode feeds.

Considering the price for the ADL or the trouble controlling the Chaparral, many hobbiests might opt for two 621's, Ck1's, C2's, 741's, etc.

 

[nycrich]

Thanks Pendragon & Anole for the advice. I think for the meantime I will stick with taking out the dielectric plate for the circular sats. My dish is within reach. I'm in the process of getting an AZBOX so my funds are committed on that project.
Back in 2000 when FTA DVB was now emerging I had a 5.3ft solid dish, Chaparral Corotor+, and a separate box used to control polarity& skew. In those days the Satcruiser was popular.
I would wire the actuator(Hal 18inch actuator) and skew motor(Chaparral motor) to the separate motor controller. I was able to scan from 12W to 139W. If I was on a sat I would change polarity for that transponder and skew the motor until the signal peaked (motor box had remote). It was time consuming moving from V to H Transponders and adjusting the skew. Most of the older analog receivers can do the job of moving the dish and controlling the skew, however the only issue is that they are not accurate(reed counter issues, as discussed in previous threads).
I'll stick with just taking out the plate. However I will look into other ideas (European sites) and post my results when I get into that project. Thanks again guys.........Rich

 

[Anole]

I think for the meantime I will stick with taking out the dielectric plate for the circular sats.
My dish is within reach.

However I will look into other ideas (European sites) and post my results when I get into that project.

Wax on, wax off:
That's "insert for circular, remove for linear". -

Euro Folk:
Yes, let us know what you run across.
I've seen some strange things on foreign web sites and forums.

Mumbo Jumbo:
I once wrote (quite strongly) that, learning the lingo, is the hardest part of FTA.
So, for anyone reading this thread later, let me take a second to clarify something about the various LNBF's listed above.

...many hobbyists might opt for two 621's, Ck1's, C2's, 741's, etc.

BSC 621 comes in at least three flavors, does C & Ku, and may be sold by Sadoun or WSI
DMX 741 comes in two flavors, and may be available from WSI and Sadoun
CK-1 does C & Ku, and is handled by SatelliteAV and Sadoun
C2 is a dual output, C band only LNBF, available from SatelliteAV and Sadoun.
So, if you need more info, the links shown will help you find these products.

And anyone with a question is welcome to read the reviews we've posted, search for discussions, or just simply: ask!

 

[nycrich]

I saw last night Sadoun is selling the C2 Dual for $34 + free shipping. I bought it immediately, good deal. Comes with dielectric insert and has dual C band output.

 

[tanka]

my friend I have one corotor 2 + dialectric plate new in the box and no good lost signal on the vertical and horizontal .I have c+ku band for 18 years and free to air .My experiense ites no If you have c+ku and circulare not working any good Ok in circulare bed on the v+h.

 

[DK_Sat]

On pendragon post lots of good info on circular feedhorne

I have being using a wideband Corotor II plus for over 20 years
First the dish need to be tracking the ark then the installation of the Corotor II need to have the right FDR and the right Focal point to get the max signal from a wideband Corotor II plus or any feedhorne

 

[nycrich]

How is reception of both linear and circular signals? I understand that you still need to put in the dielectric plate to get both signals (H, V, R, L). That is of course if you have it set up for all polarities with the dielectric plate. Chaparral claim low lost like all manufacturers. I have a lnb C/Ku (DMX741U) with dielectric plate installed for all polarities, but with the plate in, the linear signals(V, H) get dergraded, unless I take the plate back out.

 

[DK_Sat]

I have super good signal with my wideband Corotor II plus on V/H/L/R my dish is tracking from 27.0w to 137.0 w i am using CAL Amps C/KU LNBs if you want the max signal on all polaratis go with wideband Corotor II plus , If you want something chip and not reliable and imitation garbage go with c/ku LNBF

 

[pendragon]

I'm not putting down the Corotor II+ because no other single FTA feed in production that I am aware of can switch between all four polarizations from the comfort of your home. However this convenience comes at a price, and that price is apparently exacted by the dielectric insert and the rotor design itself through small losses in CNR vs. dedicated orthomodes.

I have not tested this Corotor and only had the non-wideband version on one of my dishes for a very short time (hours). It's quite tedious to make exacting measurements when comparing C-band feeds, and I have not run into anyone who has done a direct shootout between the Corotor II+ and circular/linear orthos. But I have collected a fair amount of anecdotal information from people who have used all over many years.

The consensus is that a virgin rotor (no dielectric plate) delivers about 0.5-1.0 dB lower CNRs than an orthomode linear feed. There is apparently a further 1 dB loss to circularly polarized signals compared to high-end circular ortho feeds. With the dielectric plate in the Corotor II+ some have suggested losses on the linear side, but these claims have been less clear to me. It makes physical sense, though. These are not scientific facts and should be taken with a good dose of skepticism, but the prevailing opinions seem to be you can expect 1-2 dB of CNR loss from Corotors depending on the configuration.

Low-end C-band LNBFs (voltage switched polarity) do not suffer from rotor losses, so one must be cautious in assuming that a Corotor will always do better. However these LNBFs still have dielectric plate losses on circular C-band and not all may have as good LNBs as one can place on a rotor feed. They are a lot more user friendly with modern FTA receivers. If you have one of these units and are happy with its linear performance, I would recommend getting another and inserting a dielectric plate in one for a siamese configuration over a Corotor II+. But only if the feedhorns butt right against each other so you have only miniscule offset losses. See Anole's link to my thread on such.

Regardless, the keys to C-band success are alignment, alignment and alignment. A crummy feed can look decent in a well aligned system, but an incredible feed in a poorly aligned configuration will always be horrible.

 

[tdti1]

I like my corotor II plus wideband, been using it for years, my c/ku band reception is not bad.

 

[Anole]

.... I have a lnb C/Ku (DMX741U) with dielectric plate installed for all polarities, but with the plate in, the linear signals(V, H) get dergraded, unless I take the plate back out.

. . . uhhhhhmmmmm . . . that's right.
I thought we covered this in the first page . . .

The wide band corotor leaves the plate in at all times for all (4) polarities.
The electrically controlled LNBFs must have the plate removed for linear operation.